Suresh, KumarSingh, Gurpreet2020-01-242020-01-242019-07http://krishikosh.egranth.ac.in/handle/1/5810141678The present investigation was conducted in an ongoing long-term experiment on effect of continuous use of herbicides on weed shifts in rice- wheat system at the Research Farm of Department of Agronomy, Forages and Grassland Management, CSKHPKV, Palampur during 2016-17 and 2017-18. Nine treatments viz., Farmer’s practice, continuous use of herbicide in rice and continuous or rotational use of herbicide in wheat, continuous use of herbicide in rice with substitution of 25 percent N though Lantana and continuous or rotational use of herbicide in wheat, rotational use of herbicide in rice and continuous or rotational use of herbicide in wheat and rotational use of herbicide in rice with substitution of 25 percent N though Lantana and continuous or rotational use of herbicide in wheat were evaluated for two years (2016-17 and 2017-18) with three replications. Ammannia baccifera and Cyperus sp. were the most dominant weeds constituting (11.97 and 14.54%) of the total weed flora during Kharif 2016 and 2017, respectively. These were followed by Scirpus sp., Cyperus sp. and Monochoria vaginalis, during 2016 and Ammannia baccifera, Scirpus sp., and Monochoria vaginalis, during 2017. Avena ludoviciana was the most dominant weed constituting 20.22 and 18.61% of the total weed flora during Rabi 2016-17 and 2017-18, respectively followed by Phalaris minor (19.26 and 17.69%), Lolium temulentum (19.08 and 15.84%), Poa annua (16.02 and 17.51%), Vicia sativa (10.68% and 8.5%) and Polygonum alatum (1.5 and 6.94%). Significantly lower total weed count, total weed dry matter accumulation and NPK depletion by weeds was recorded in ‘continuous use of herbicides in both the crops with substitution of 25 per cent N through Lantana in rice’ and ‘rotational use of herbicide in both the crops with substitution of 25 per cent N through Lantana in rice’ during both the year of study in rice and wheat, respectively. In rice, significantly higher plant height, dry matter accumulation, leaf area, leaf area index, CGR, yield attributes, yield and nutrient uptake during both the years were recorded in ‘continuous use of herbicide in both the crops with substitution of 25 per cent N through Lantana in rice’. In wheat, significantly higher plant height, plant population, dry matter accumulation in root, shoot, leaves and CGR were recorded in ‘rotational use of herbicide in both the crops with substitution of 25 per cent N through Lantana in rice’ during both the years. Treatment effects were not significant for RGR and NAR for both rice and wheat. The system’s net return and net return per rupee invested were maximum in rotational use of herbicide in both the crops with substitution of 25 per cent N through Lantana in rice’ during both the years. On an average rotational use of herbicide in both the crops with substitution of 25 per cent N through Lantana in rice’ was found to be the best treatment for getting higher productivity and profitability.ennullThesis